Polyester-carbonates are well known high molecular weight thermoplastic materials which exhibit many advantageous properties. These properties render the polyester-carbonate resins useful as high performance engineering thermoplastics.
The polyester-carbonates are known to be susceptible to degradation under extreme heat and moisture which causes a reduction in properties including impact strength and appearance. This problem tends to reduce the use of these materials in applications where heat and moisture are present. The applicants have found that the addition of a minor amount of a linear low density polyolefin to a polyester-carbonate will result in a molding composition that will substantially maintain the impact strength of the polyester-carbonate when the composition is subjected to heat and moisture. This improved performance property has been demonstrated by tensile impact tests and unnotched impact tests after exposure to 82.degree. C. water and superheated steam.
The increased stability is achieved without substantially depressing the heat distortion temperature of the polyester-carbonate resin. This is an advantageous result which makes the use of the linear low density polyolefins in combination with polyester-carbonate resins very attractive.